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I re-factored some code today, and in the process managed to create a lock deadlock for myself. In the end it turned out to be an exception was being thrown when a lock was held, and adding a try / finally resolved the real underlying problem. However, in the process I ended up writing this little helper that I am sure will be useful in the future.

import gflags
import thread
import threading
import traceback
import logging

...

FLAGS = gflags.FLAGS
gflags.DEFINE_boolean('dumplocks', False,
                      'If true, dumps information about lock activity')
...

class LockHelper(object):
  """A wrapper which makes it easier to see what locks are doing."""

  lock = thread.allocate_lock()

  def acquire(self):
    if FLAGS.dumplocks:
      logging.info('%s acquiring lock' % threading.currentThread().getName())
      for s in traceback.extract_stack():
        logging.info('  Trace %s:%s [%s] %s' % s)
    self.lock.acquire()

  def release(self):
    if FLAGS.dumplocks:
      logging.info('%s releasing lock' % threading.currentThread().getName())
      for s in traceback.extract_stack():
        logging.info('  Trace %s:%s [%s] %s' % s)
    self.lock.release()

Now I can just use this helper in the place of thread.allocate_lock() when I want to see what is happening with locking. It saved me a lot of staring at random code today.